In the preparation of thin film transistor liquid crystal display (TFT-LCD), polyimide (PI) coating process is a very important part. The PI coating is typically carried out by use of polyamic acid or polyimide solution in a manner of passing through a photosensitive resin plate (alignment film printing plate) or spraying. When the PI coating is finished, after leveling, pre-curing and curing, orientation is carried out through friction orientating or light curing orientating, and then by dropping the liquid crystal, cell assembling and cutting, a conventional TFT-LCD liquid crystal cell is formed. During the course of PI coating, there might be defects such as pinhole-like defects caused by unevenness of the substrate surface. Such pinhole-like defects in the TFT-LCD are often embodied as white or black spots.
At present, the aforementioned problem is mainly solved by making repairs after the defects appear.